1. Field of the Invention
The present invention relates to a color filter for use in a flat panel display and, particularly, to a structure of a color filter for a liquid crystal display device.
2. Description of the Prior Art
As a color filter for a liquid crystal display device, there are two types, in one of which a color filter is formed on the side of an opposing substrate opposing to a Thin Film Transistor (referred to as xe2x80x9cTFTxe2x80x9d, hereinafter) substrate and in the other of which a color filter is formed on the side of the TFT substrate. FIG. 1 is a cross section of the first example of a color filter to be formed on the side of an opposing substrate. As shown in FIG. 1, the color filter has a structure including a transparent substrate 41, a black matrix 42 formed on the transparent substrate 41 by forming a lattice pattern with using photolithography, etc., a color layer 46 printed or covered by using photolithography with color materials such as dyes, organic pigments or inorganic pigments such that the color materials fill spaces between lattices of the black matrix 42, a resin film layer 44 covering the color layer 46 and the black matrix 42 and a pixel electrode 45 formed on the resin film layer 44.
FIG. 2 shows a cross section of the second example of the color filter to be formed on the side of the opposing substrate, which is disclosed in Japanese Patent Application Laid-open No. H5-119306 and may belong to the same category as that of the present invention. The second example, which is called as Color filter-On-TFT (COT), includes a transparent substrate 61, a color layer 66 formed on the transparent substrate 61, a resin film layer 64 formed on the color layer 66, an upper titanium dioxide (TiO2) layer 73 formed on the resin film layer 64 and a pixel electrode 65 formed on the upper titanium dioxide layer 73. The upper titanium dioxide layer 73 is formed for improving adhesion between the resin film layer 64 and the pixel electrode layer 65.
FIG. 3 shows a cross section of the third example of the so-called color filter-on-TFT where a color filter is formed on the side of the TFT substrate, which is disclosed in EURO DISPLAY ""99 LATE-NEWS PAPER P77-80. The third example includes a transparent substrate 81, a TFT formed thereon, which is composed of a gate wiring 87, a gate insulating film 88, a semiconductor film 91, a drain wiring 89 and a source wiring 90 and a protective insulating film 92 covering the TFT. As shown, an upper portion of the TFT except the protective insulating film 92 has a similar structure to that shown in FIG. 1. That is, a color layer 86 having an opening portion above the semiconductor film 91 of the TFT is formed on the protective insulating film 92 and the opening portion is filled with a black matrix 82. Further, the color layer 86 and a black matrix 82 are covered by a resin film layer 84 and a transparent pixel electrode 85 of ITO (Indium Tin Oxide).
However, in a liquid crystal display of such as IPS (In-Plane-Switched) system, which has no pixel electrode or the COT shown in FIG. 2, there is a possibility that a portion of the resin film layer 84 functioning as the over coat is exposed to the liquid crystal layer depending on a layout of the pixel electrode 85.
If the resin film layer 84 is exposed partially, oxygen contained in the liquid crystal layer diffuses through the exposed portion into the color layer 86. Oxygen molecules reached the color layer 86 are activated by excitation energy of external ultraviolet ray, so that color materials such as organic pigments used in the color layer are decomposed, resulting in color degradation.
Therefore, when a layer, which is formed above the color layer 86 in order to shut out oxygen molecules from the color layer 86, does not cover the color layer 86 completely, i.e., some part of the layer is opened above the color layer 86, some problems as mentioned above occurs in the conventional color filter substrate for liquid crystal display.
The structure including the upper titanium dioxide layer 73 such as shown in FIG. 2, which may block external ultraviolet ray, is known. In such color filter substrate, however, there is a possibility that the color layer 66 is degraded by activated oxygen dissolved in the resin film layer 64.
An object of the present invention is to provide a structure of a color filter which is not degraded by ultraviolet ray or oxygen on a substrate with a color filter.
In order to achieve the above object, the color filter according to the present invention includes a basic light shielding structure which blocks ultraviolet ray incident on a color layer formed on a substrate at least at the upper side of the color layer. The basic light shielding structure includes two types of light shielding structures, wherein the first light shielding structure blocking ultraviolet ray incident on the surface of the color layer at the upper side of the color layer by directly covering the surface of the color layer only at the upper side of the color layer and the second light shielding structure covering both on and below the color layer.
The first light shielding structure includes the color layer formed on the substrate and an upper light shielding layer, which directly covers the surface of the color layer at the upper side of the color layer.
The second light shielding structure includes an upper light shielding layer formed on the color layer and a lower light shielding layer formed below the color layer, blocking ultraviolet ray by both of the upper light shielding layer and the lower light shielding layer from the color layer. Furthermore, the upper light shielding layer covers the surface of the color layer at the upper side of the color layer, and more concretely covers directly the surface of the color layer at the upper side of the color layer.
The color filter according to the second light shielding structure of the present invention includes a substrate, a color layer on the substrate, a gate electrode and a semiconductor layer which composes a channel region of a TFT between the substrate and the color layer, the color layer being formed above the TFT, an upper light shielding layer covering the color layer. The color layer includes an opening area above the channel region of the TFT. The color filter further includes a black matrix layer formed between the TFT and the upper light shielding layer. The black matrix layer covers at least the opening area of the color layer and locates above the channel region of the TFT.
The light shielding structure of the color filter includes a titanium dioxide layer.